FAQ

Frequently asked questions

General

AniForm Engineering BV is a company founded in 2011 as a University of Twente spin-off. AniForm Engineering BV is now located at the Business & Science Park in Enschede, the Netherlands. AniForm’s expertise includes forming predictions of fibre reinforced composites, material characterisation under forming conditions, and process optimisation with respect to formability. AniForm Engineering develops forming simulation software and offers engineering services to deal with composite forming cases.

AniForm Engineering developed the AniForm Suite software, which is based on the finite element method (FEM). AniForm Suite includes AniForm PrePost and AniForm Core. AniForm PrePost is a graphical user interface to model the composite forming process. The pre-processing mode enables you to set up a new simulation model, whereas the post-processing mode enables you to analyse the simulation results. AniForm PrePost invokes simulations by pushing the models to AniForm Core.

AniForm Core is an implicit solver. Reaching convergence with an implicit solver always obeys the balance between internal and external forces, which is not the driving condition for explicit solvers. Additionally, AniForm is especially tailored to deal with high anisotropy (fibre reinforced composites) and large deformations, which cannot be done properly with standard FEM software you may know. AniForm also considers the material behaviour, which is not possible when dealing with the kinematic draping approach. Years of research on laminate deformations and material behaviour of composites led to a successful modelling approach that is used in this software.

Modelling forming cases

You will need to model the entities and capture the phenomena of which you think they will affect the laminate deformations significantly.

The set up of a basic forming simulation starts by modelling the contact surface of the tooling that will make contact with the blank during forming. Modelling the complete tooling is not always required to obtain a reliable forming prediction. The tooling surfaces require a discretised representation of triangular elements, because the modelling technique is based on finite elements.

Next, a surface representation of the blank/laminate is required. Also here, the surface must be discretised with triangular elements. In AniForm PrePost, material properties and a layup can be assigned to this laminate representation.

You may also involve aided tooling such as blank holders. These can be imported as discretised surfaces as well. Such surfaces can be force or displacement controlled throughout the simulation. Also tensioners/springs can be applied.

Finally, you will need to supply the process conditions. The software needs to know what tooling moves and according to which speed.

Tooling surfaces are discretised by a mesh of triangular elements, which make contact with the blank during forming. Tooling is usually modelled as being rigid, which is generally a good approach when an indication of the material’s formability with respect to the tooling geometry needs to be obtained.

In AniForm PrePost, the blank/laminate also needs to be represented by a single layer of triangular elements. When a simulation is invoked, the layer of elements will be duplicated and offset according to the number of plies defined in the layup builder form. The imported mesh representing the laminate may contain mesh sections. An individual layup can be assigned to each section, thereby offering the user the ability to model tailored blanks.

No, AniForm PrePost can import triangular mesh representations of the tooling and laminate surfaces. Most CAD software can export surfaces to an .stl mesh, which can be imported in PrePost. The laminate will, however, be remeshed in PrePost to ensure predictions of sufficient quality.

3-node shell and contact elements are used to describe the ply deformations and interface slippage. When conducting more advanced simulations through manually compiled AniForm input files, also 4-node tetrahedra with linear shape functions and 10-node tetrahedra with quadratic shape functions are supported.

Contact logic at each ply-ply or tool-ply interface is described by paired contact elements (slaves and masters). The robust penalty method is used to minimise the penetration of the surfaces at the interface. Next to the penalty model, additional in-plane models can be assigned to model the traction at the sliding interfaces.

Yes, the imported mesh representing the laminate may contain mesh sections. An individual layup can be assigned to each section. The properties of a layup are the number of plies, ply orientations, and material properties assigned to each deformation mechanism. Material properties are separately assigned to the in-plane, out-of-plane, and interface deformation mechanisms. With the aid of the global ply numbering feature, a wide variety of tailored blanks can be modelled.

Also, tailored laminates can be reconstructed from "automated fibre placement" xml files, which contain fibre/tape paths defined in space and according to a placing sequence. Such files can for example be generated by fibre/tape placement software.

Yes, as long as the segments are described by different meshes. The meshes will be converted to tools in AniForm PrePost. In the loading section of AniForm PrePost, these tools can individually be subjected to any motion and speed.

Material modelling

Any composite material of which its material behaviour related to the significant deformation mechanisms is known. These mechanisms are considered at the in-plane, out-of-plane and interface levels. AniForm is tailored to deal with continuous fibre reinforced laminates. When modelling a ply of a laminate, it can be equipped with a family of fibres having a certain orientation.

Uni-directional plies (UDs) can be described when having its material behaviour under shear, bending, ply-ply slip, and tool-ply slip conditions. At the in-plane level, a single family of fibre directions is added.

Wovens, fabrics, or textiles having two fibre directions also require its material behaviour under shear, bending, ply-ply slip, and tool-ply slip conditions. At the in-plane level, two families of fibre directions are added.

Bi-or tri-axial non crimp fabrics (NCFs) are regarded as two or three uni-directional (UD) plies stacked on top of each other. Each ply is equipped with the material behaviour at the in-plane, out-of-plane, and interface levels. At the in-plane level, one family of fibre directions represents the UD fibres, whereas another family of fibre orientations with a lower stiffness represents the major stitching direction.

In AniForm Prepost, you can simply import a single ply mesh representing the 2D blank. Next, a layup can be created with the layup builder form or a pre-defined lay-up can be imported (AniForm Layup file, .afl). The layup can be assigned to the single ply mesh. When you start the simulation, the ply will be duplicated and offset according to the number of plies defined in the layup builder form.

Each ply in a laminate can thus be modelled separately, which opens up the possibility that neighbouring plies can slide relatively to each other. When you have a laminate comprising many plies (for example 16, 24, or more plies), you may think of a ply lumping procedure. The many plies will then be represented by fewer plies (for example 4, 5, 6, or more), whereas the overall behaviour is close to equivalent with respect to a simulation where you would model all plies. Of course, you will lose a bit more detail, but that is the trade-off when coarsening the model.

Regarding the ply deformations, after quite some time of research we have established the following division of deformation mechanisms of a composite ply: in-plane, out-of-plane (bending), and interface mechanisms. This approach is used because one material model cannot be used to describe the total deformation behaviour of a ply at once, which is for example the case when dealing with metals.

Yes, AniForm’s underlying equilibrium equation considers time-independent and time-dependent constitutive behaviour, as well as contributions of inertia. Time-dependent models are for example the viscous models, which can be used to describe in-plane, out-of-plane (bending), and interface deformations. Inertia terms are determined by the densities (eventually determining the mass of an element) assigned to the membrane elements (translational inertia) and the Discrete Kirchhoff Triangles (rotational inertia).

Material properties and characterisation

You will need a description of the material under forming conditions, which indeed results in different properties compared to those used to describe the material’s solidified state. In-plane, out-of-plane (bending), and interface mechanisms need to be described separately.

Characterisation of the material under forming conditions can be done by dedicated characterisation tests. AniForm and partners have developed several tests to characterise the significant in-plane, out-of-plane and interface mechanisms. More information can be found here.

Experimental curves related to the characterisation of a particular mechanism can be described in the forming model when AniForm material models are fitted onto these curves. Currently available models can be found here. The AniForm Matfit program enables you to fit your experiment curves.

Advanced usage

AniForm PrePost is designed to quickly set-up a simulation. An input file (.afi) is automatically generated when invoking a simulation. The .afi file is read by AniForm Core, which subsequently solves the model.

AniForm Core is a very flexible solver that allows you to perform highly advanced simulations. For example, you can use AniForm PrePost to set up the initial model after which you can manually edit the generated .afi file to convert the basic model into an advanced simulation model.

The blank geometry can be edited in your CAD software. Select the resulting surfaces, export it to an .stl mesh, and import it in PrePost. Splits, cuts, and darts can be added within a few clicks in PrePost. See our key features for more information.

Yes, meshes representing the surfaces of the blank holders can be imported. When converting these in AniForm PrePost to a rigid tool, these can be force or displacement controlled. Tensioners/springs and grippers can be added within a few clicks. See our key features for more information.

Almost, this feature is currently in the testing phase. It must be noted that using the material behaviour at the constant forming temperature already captures 80% of the forming effects that appear in practice. Adding temperature dependency would increase the prediction quality to max 90%, depending on the particular case. In other words, the isothermal approach gives sufficient information about the material’s formability in the majority of the cases we have dealt with.

We recommend to conduct this analysis in standard FEM software such as Abaqus. The Abaqus CAE model can be updated with the material re-orientation as predicted by AniForm.

Mainly, spring-back/forward can be attributed to three phenomena:

- Chemical effects of the polymer, shrinkage.

- Mechanical stresses induced by the press forming process, which are then frozen-in when the material solidifies. When releasing the part from the tooling, the residual stresses will (partly) be relaxed, resulting in shape distortions.

- Thermal effects due to temperature gradients and differences in thermal expansion coefficients.

Hardware

AniForm Core runs basically on any pc with a Microsoft windows platform. AniForm Core is a parallelised solver, such that the availability of more processor cores results in shorter simulation times. You may use AniForm Core on your notebook but such devices are usually not optimised to intensively solve a large number of equations. Large servers can be used to run simulations on, however, these can be costly. An intermediate solution could be an advanced pc with extended memory and advanced processors, such as the examples listed in the hardware advice section here. AniForm PrePost uses the video driver functions for optimal performance. It requires the pc where you run AniForm PrePost to satisfy certain video card requirements, which can be found here.

The AniForm Suite components (AniForm PrePost and AniForm Core) are designed to promote an efficient workflow when working on forming optimisation cases. AniForm Core is usually installed on an advanced computer tailored to perform intensive calculations. However, this is generally not the machine the user works on by default. AniForm PrePost can be installed on the less advanced machine of the user, where simulation models can be prepared prior to staring the calculations. Once the model input is ready, the user may transfers the generated AniForm input file (.afi file) to the more advanced computer where AniForm Core is located on. When more designers work on optimisation cases simultaneously, it is advised to license multiple AniForm PrePosts.